[double00]

I read a fellow modeller's tip on how to clean coach windows and remove minor scratches on the windows surfaces.
I must admit, this tip was taken with a pinch of salt - as the substance recom-
mended by this modeller was "toothpaste".
You simply rub a small amount of toothpaste, applied using finger, on the window surfaces and allow a few minutes, then wash off toothpaste with luke warm clean water.
Then wipe dry with a lint free cloth, leaving a nice clean window surface.
Anyone in doubt, can always try this out on an old coach no longer being used.

 

[Rail-Rider]

I would think toothpaste certainly worth trying as it is mildly abrasive and water soluble. Probably best to avoid the "whitening" types though - full of bleach!
I'm not sure that there is any point in leaving it on for a few minutes though. There is no solvent action - it's the physical abrasion that does the trick.

An alternative is 'T-Cut' used for tarting up mildy scratched or faded paintwork on full size cars. Again, elbow grease is the secret, though you wouldn't need a heck of a lot on little train wndows!